12-15 July 2011
Saint George Hotel
Africa/Johannesburg timezone
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Enhanced green emission from UV down-converting Ce3+-Tb3+ co -activated ZnAl2O4 phosphor

Presented by Mr. Kamohelo George TSHABALALA on 14 Jul 2011 from 09:00 to 09:15
Type: Oral Presentation
Session: CMPMS1
Track: Track A - Condensed Matter Physics and Material Science


<p>Rare–earths (Tb<sup>3+</sup> or Ce<sup>3+</sup>) doped zinc aluminate (ZnAl<sub>2</sub>O<sub>4</sub>) nanocrystals were successfully prepared by a modified combustion method using urea (CH<sub>4</sub>N<sub>2</sub>O, 99–99.5%) as fuel and characterized to investigate down-converted emission by energy transfer from Ce<sup>3+</sup> to Tb<sup>3+</sup> . The post-preparation annealing of the samples was carried out in a reducing atmosphere of 4%H<sub>2</sub>/96%N<sub>2</sub> mixture at an elevated temperature of 700<sup>0</sup>C for 4 hours. This was meant to reduce non-emitting Ce<sup>4+</sup> to Ce<sup>3+</sup> and also to improve crystallinity. As confirmed by X-ray diffraction (XRD) data, the materials were highly crystalline and the XRD patterns were consistent with the closed-packed face centered cubic spinel structure of ZnAl<sub>2</sub>O<sub>4</sub>. The photoluminescence excitation and photoluminescence data collected when ZnAl<sub>2</sub>O<sub>4</sub>:Ce<sup>3+</sup>,Tb<sup>3+</sup> samples, with different concentrations of Ce<sup>3+</sup> and Tb<sup>3+</sup> ions, were excited at different wavelengths (230―325nm) showed that green emission of Tb<sup>3+</sup> was sensitized by Ce<sup>3+</sup>, i.e. there was energy transfer from Ce<sup>3+</sup> to Tb<sup>3+</sup> resulting in improvement of green emission due to the <sup>5</sup>D<sub>4</sub> → <sup>7</sup>F<sub>5</sub> transitions of Tb<sup>3+</sup> ions. This study therefore, sets out to discuss the sensitizing effect of Ce<sup>3+</sup> and the effect of post annealing on the structure of ZnAl<sub>2</sub>O<sub>4</sub>:Ce<sup>3+</sup>,Tb<sup>3+</sup>. The results indicate the potential of the phosphor powders for applications in luminescent display panels and further development as UV down-converters for improved performance of conventional photovoltaic cells.

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Room: Parthenon

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